1. Field of the Invention
The present invention relates to a photographic material for use in forming a photomask and a method for producing a photomask using same. More particularly, it relates to a photographic material for use in forming a photomask having excellent quality using a silver halide photographic emulsion layer as a light-sensitive material and to a method for easily producing a photomask having high quality using the photographic material.
2. Description of the Prior Art
It is known in the field of printed circuit fabrication or microelectronic fabrication to use a photomask in forming images utilizing a photoresist method. Heretofore, silver images or chromium images have often been utilized in the photomask. Silver images are obtained by imagewise exposing a photographic light-sensitive material (so-called emulsion mask) provided on a glass plate, followed by conventional photographic processings (e.g., development and fixing). On the other hand, chromium images are formed by providing a vacuum-deposited chromium layer on a glass support and etching the chromium layer using a photo etching method. That is, a photoresist is coated on the chromium layer and, after exposing through a photomask superposed thereon (contact method) or after projecting a photomask on the photoresist (projection method), the photoresist is development-processed to form a resist image, followed by etching the chromium layer.
Since an emulsion mask has high sensitivity, it is suitable for preparing a photomask. However, the resolving power of the photomask obtained is inferior to that of a chromium mask using the projection method due to scattering of light by the silver grains, great thickness of the silver halide emulsion layer and silver particles after development. A photomask utilizing silver images is inferior in resolving power for the following additional reason. That is, since the developed emulsion thickness is larger at silver image areas than at nonimage areas, gaps or spaces are formed at the contact surfaces upon intimately contacting the photomask with the photoresist layer in order to form a resist image, thus markedly reducing the resolving power. In addition, a photomask formed by a silver image has such a small mechanical strength that it is easily damaged. Also, since a silver image does not transmit visible light, positioning of the mask is difficult.
On the other hand, a chromium mask using the contact method is inferior to a photomask obtained with silver images in resolving power, since the resolving power of a chromium mask is reduced on exposing a photoresist layer and upon etching the vacuum-deposited chromium layer. Also, with a chromium mask using a projection method, the photoresist layer has such a low sensitivity that exposure requires too much time, and thus it is difficult to use a chromium mask in this manner industrially. In addition, since the etching method results in environmental pollution through discharge of the used etching solution, it has become difficult to employ the etching method on an industrial scale.